Photography using silver halides has long been widely used because of excellence in photographic characteristics, such as sensitivity and gradation control as compared with other photographic techniques, such as electrophotography and diazo processes. For simpler and faster image formation with silver halide photographic materials, conventional wet processes using a developing solution, etc., have recently tended to be replaced by dry processes using heating, etc.
Many processes for dye (color) image formation have hitherto been proposed. For example, processes for forming a dye image by coupling between an oxidation product of a developing agent and a coupler include use of p-phenylenediamine reducing agents and phenolic or active methylene couplers as described in U.S. Pat. No. 3,531,286; use of p-aminophenol reducing agents as disclosed in U.S. Pat. No. 3,761,270; use of sulfonamidophenol reducing agents as described in Belgian Pat. No. 802,519 and Research Disclosure, Vol. 137 (September, 1975), pp. 31-32; and use of sulfonamidophenol reducing agents and 4-equivalent couplers as described in U.S. Pat. No. 4,021,240.
Research Disclosure, RD No. 16966 (May, 1978), pp. 54-58 describes a process comprising forming a silver salt of a dye having introduced therein a nitrogen-containing heterocyclic ring and causing the silver salt to release the dye upon heat development.
For positive image formation by the silver dye bleach process, useful dyes and processes of bleaching are described, e.g., in Research Disclosure, RD No. 14433 (April, 1976), pp. 30-32, ibid., RD No. 15227 (December, 1976), pp. 14-15, U.S. Pat. No. 4,235,957, etc.
Further, dye image formation using leuco dyes is described, e.g., in U.S. Pat. Nos. 3,985,565 and 4,022,617.
However, the above-described various processes generally require a relatively long time for development and produce images of high fog and low density.
In order to eliminate such disadvantages, an image formation process using silver halide, in which a mobile dye is imagewise formed and then transferred to a dye-fixing layer, has been proposed, as disclosed in Japanese Patent Application (OPI) Nos. 58543/83 (U.S. Pat. No. 4,500,626), 79247/83 (U.S. Pat. No. 4,483,914), 149046/83, and 149047/83 (the term "OPI" used herein means "published unexamined application").
The conventional heat-developable light-sensitive materials have disadvantages in that the development speed is not sufficient and that the maximum density of a resulting image is not sufficiently high. Further, attempts to accelerate development or to increase the maximum density by altering development conditions, such as a heating temperature, a heating time, etc., result in an increase of the minimum density, i.e., fog, even though an improved maximum density may be attained. In addition, satisfactory images cannot be stably obtained unless the development conditions are maintained constant. In other words, developability is unstable with respect to variation from the optimum development conditions.